= new reply since forum marked as read
and unless it shows how deep the vein is, it's not really going to help. You feel for diameter, direction and depth. It doesn't tell you the consistancy of the vein; whether its rubbery and likely to roll. And it doesn't provide any visual cues. By the time you finish running the thing over somebody's arm, turn back to set it down, turn back to stick, you'll have lost that image. And if you're drawing from a hand, location of bone is critical. 
Two things cause the pain. One is inadvertently hitting a nerve; since they aren't marked, it's not like we can choose to avoid them. The other are those who think they are being gentle by going slowly and "fishing" for the vein, instead of getting a good feel of where it is and then just going for it.
I wish I could say the same for myself. I've hit a nerve while injecting my insulin more than once. 
